The terrorist hijacking and suicide crashes of four U.S. civilian airliners on Sep. 11, 2001, were tragic and unforeseen. The inability of the air traffic control and civil defense infrastructure to respond effectively to the situation as it developed was due, in part, to limitations of the current radar-based surveillance infrastructure.
Because of timing delays and accuracy limitations inherent in the design of current radar-based air traffic control systems, controllers are unable to determine the real-time intent of aircraft they are tracking. Moreover, current radar surveillance systems depend on transponder responses from the aircraft to operate at maximum efficiency. The September 11 terrorists disabled or turned off some aircraft transponders in the cockpit of the hijacked aircraft, making it difficult to track the aircraft. This, combined with the limitations of current surveillance radar systems, made it nearly impossible for controllers to realize that three of the aircraft had turned into collision courses with ground targets.
Thus, there is a need for an aircraft surveillance system that cannot be interrupted by unauthorized persons. There is a further need for an improved surveillance system that is configured to warn ground controllers when an aircraft acts outside of cleared parameters. Furthermore, there is a need for systems that alert ground controllers if someone in the aircraft is attempting to send a false signal to deceive the controllers into believing that the aircraft is following a planned course when in fact it has been diverted. In addition, there is a need for an improved surveillance system that allows pilots to quickly and reliably issue a distress signal upon realizing that their aircraft is in danger of being hijacked.